Science has shown us that a number of organisms use the stars for navigation: songbirds, harbor seals and, of course, humans. But a new study by a team of Swedish and South African researchers published today in the journal Current Biology indicates that a rather unexpected creature can be added to this list—the lowly dung beetle.
The beetles are known for creating small balls made of animal feces (i.e. dung) and rolling them in straight lines over long distances. They do this because the dung is their main food source—and other beetles often try to steal the dung once it’s been rolled into a ball. The surest way of retaining the valuable dung once it’s been packed into a ball is to move it away from the original dung pile as quickly as possible:
Researchers, though, have long been mystified by the tiny beetles’ ability to roll the dung balls in straight lines at night. “Even on clear, moonless nights, many dung beetles still manage to orientate along straight paths,” said lead author Marie Dacke of Lund University in Sweden. “This led us to suspect that the beetles exploit the starry sky for orientation—a feat that had, to our knowledge, never before been demonstrated in an insect.”
To test the hypothesis, the scientists set up a circular ring with a radius of about 4 feet outside and placed a dung pile at the center. They tested how long it took the beetles to reach the ring from the center—a measure of how straight their paths were—and found that their navigational abilities were relatively similar with either a full moon in the sky or at least a clear view of the stars. When they placed tiny blinders on the beetles’ eyes or subjected them to overcast conditions, though, their paths became much more windy.
Next, they placed a number of beetles in a planetarium and performed a similar test. Their paths were straightest with all the stars turned on, but were almost as true with just the Milky Way—indicating that they are particularly dependent on the Milky Way’s streak of light for navigation.
When the researchers turned on a large number of dim stars—many of which lie in the band of the Milky Way—the beetles’ navigation speed still remained similar. It was only when they left on just 18 of the brightest stars that their pathways became significantly windier.
The authors say that this proves that the beetles don’t rely on one particular star or celestial object for navigation, but rather take in the totality of the Milky Way—which appears as a startlingly bright band of light in many rural areas—to orient themselves on the ground.